The present invention relates generally to a mechanism for adjusting selected video display characteristics in a computer system. More particularly, an arrangement for controlling the number of dots that are displayed on a video screen per inch of printed output (DPI) is described.
In most modern personal computer systems, the video display monitor is controlled by a dedicated video card that has a plurality of software based display drivers. The operating system selects which display driver is to be used and then stores information about the screen characteristics (as dictated by the selected driver). That information is then used by both the operating system and any application that has the need to know any screen characteristics. One characteristic that the display driver must set is the number of display pixels that will be used to represent one inch of printed output. This is commonly referred to as the display's DPI (dots per inch). The DPI characteristics must be set in both the horizontal (X) and vertical (Y) directions. Although it is not required, it is common to use the same DPI value for both the horizontal and the vertical directions so that the displayed image is not distorted.
For a variety of reasons, the number of dots per inch indicated by the display driver to represent an inch of output commonly occupy more than an inch of screen space. One explanation is the assumption that the screen resolution is generally not as good as the resolution of printed matter so it is easier on the user's eyes when the displayed materials are larger than the printed text. Another reason may be that users tend not to sit as close to a video display as they would hold a piece of paper. In any event, the values selected by the display drivers are not always optimal for specific user needs. For example, users of desktop publishing software commonly prefer that the image displayed have exactly the same measurements as the printed output. Other users may wish to have the displays appear larger so that text can be read more easily or may wish a page (or portion thereof) to occupy a fixed portion of the screen or the entire screen.
Currently, one of the most popular operating systems for IBM PC compatible personal computers is the MS-DOS based Windows operating system marketed by Microsoft Corporation. In Windows, like most DOS based systems, it is not possible to change the displayed DPI for any particular display driver. The size of the displayed information can be altered somewhat by a variety of stop gap measures. However, none give the user real control over the display size. For example, one common approach in word processing applications is to change the font size of the text during inputting and editing. However, requiring the user to change font sizes is inconvenient and can lead to all kinds of formatting difficulties. Another approach is to switch the screen resolution. However, (in order to switch the screen resolution, it is typically necessary to exit any open application(s), exit Windows in Windows based systems) and then change the screen resolution in DOS. This is typically accomplished by loading a new driver program, or in the case of changing the screen resolution using a multi-resolution driver, the application requesting the new resolution saves the desired resolution values to the disk before exiting Windows. After the new driver has been loaded (or the appropriate resolution values saved), both Windows and the desired application programs must be restarted. Obviously, this procedure is slow and cumbersome. Further, when the resolution is changed, the user is limited to the DPI associated with the newly selected resolution, which may not be satisfactory.
In view of these drawbacks, a system arranged to give the user the ability to control the number of display pixels that are used to represent a given distance of print output would be desirable. Accordingly, it is an object of the present invention to provide such a system.